1. Field of the Invention
The present invention relates to a fiber output stabilizer that stabilizes output from a rare-earth doped optical fiber, particularly to a technology for compensating a decrease in output caused by photodarkening.
2. Description of the Related Art
The rare-earth doped optical fiber is used as an optical fiber amplifier or a fiber laser because the incidence of excitation light to the rare-earth doped optical fiber radiates light having a specific wavelength.
The strong excitation light is incident to the rare-earth doped optical fiber when the rare-earth doped optical fiber is used as the fiber laser. At this point, there is generated a phenomenon called photodarkening in which a loss of the rare-earth doped optical fiber increases. Conventionally, in order to compensate the increase in loss caused by the photodarkening, fiber output is stabilized by controlling an exciting current, switching a reflectance of an output unit, or using a noise-like laser (for example, see Japanese Patent Application Laid-Open Nos. 2007-190566, 2003-347629, and 2005-294806).
In the rare-earth doped optical fiber, it is characteristically confirmed from experimental results that the increase in loss caused by the photodarkening increases as a wavelength is shortened. However, in a conventional fiber output stabilizer, the wavelength dependence is not taken into account in measuring the increase in loss.
Additionally, the light of the output wavelength of the fiber laser or the light of the wavelength of the signal light is used as monitoring light, which results in a problem in that the output of the fiber laser or signal light decreases.